Microcoil Construction

ABSTRACT

A microcoil is manufactured by rolling a trace unit in such a way as to form at least one winding. The trace unit is comprised of a conductive trace attached to a flexible insulating film. A preferred embodiment of the microcoil contains both a first winding and a second winding electrically connected and spaced apart by a joining portion. The microcoil may be used for internal magnetic resonance imaging of patient by attaching the microcoil to a catheter.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.11/735,287 filed Apr. 13, 2007, which is a continuation of U.S. patentapplication Ser. No. 09/736,529 filed Dec. 13, 2000, now U.S. Pat. No.7,210,223 issued May 1, 2007. The entire disclosures of the aboveapplications are incorporated herein by reference.

FIELD OF APPLICATION

This invention relates to microcoils and their construction.Specifically, this invention relates to microcoils for use in medicaldevices used to obtain a magnetic resonance image of a region within anatural organism or patient (such as within a human) or elsewhere.

BACKGROUND

The use of magnetic resonance medical devices provides enhanced imagingwithin the region of interest and can be used for various internalprocedures including targeted drug delivery. The term microcoil or MRmicrocoil is used to denote a magnetic resonance device used for imaginginternally from a patient. This term is in contrast to MR coils that areconventionally used externally to the body for MR imaging purposes. Amicrocoil may contain one winding of electrical conductor, or multiplewindings that are spaced a distance apart from each other. Typicallymultiple windings are joined together at a predetermined spacing withthe planes of the windings parallel to each other.

The MR microcoil may be mounted at the tip of a catheter or otherinsertion device used to probe the interior of a body. The combinationof the microcoil mounted on another device provides quick and directaccess to the region where imaging is required. Medical procedures suchas image-guided and minimal access surgery, performed within smallregions of a patient's anatomy, demand the ability to visualize theinternal terrain and/or the procedure being performed by the surgeon.While alternative methods, including x-ray imaging and fiber opticviewing offer possible alternative means of performing the visualizationof terrain and the location of physical secondary devices, magneticresonance imaging methods are a particularly convenient means of doingthis, especially given the highly localized nature of the proceduresbeing performed.

As with any manufactured device, new methods of manufacturing componentsare always being pursued to enhance performance and lower manufacturingcosts. Conventionally, microcoils are manufactured by hand winding of anelectrical conductor around a mandrel, or alternatively machine windingan electrical conductor around a mandrel. The resulting winding may haveto be removed from the mandrel, and the leads for each end of thewinding must be isolated. Additionally, where multiple windings arejoined together in a device, the ends from multiple windings need to beconnected. Handling windings in the manufacturing process can causedamage to the fragile windings resulting in manufacturing yield loss.The trend of smaller devices only increases this problem. With minimallyinvasive surgical procedures, the electrical conductor diameters usedmust be increasingly smaller to provide smaller coils. These coils aremore easily damaged.

In manufacturing microcoils, there are also dimensional controlvariations within a single winding, and between windings. The diameterof the an electrical conductor used in a single winding may vary andaffect the electrical characteristics of the resulting winding.Similarly, the insulating coating around the electrical conductor mayvary in thickness and affect the electrical properties of the winding.

From one winding to another, variations in electrical conductor diameterand coating thickness are still a manufacturing variable. In addition,the number of turns from one winding to the next must be controlled bymeasuring the length of electrical conductor used in each winding. Also,the distance between windings in a microcoil containing multiplewindings must be controlled by carefully joining the ends of aconventional winding at a measured distance.

While these conventional approaches to the manufacture of windings andmicrocoils result in functioning microcoils, the process is timeconsuming with several steps. Manufacturing yield is a problem due tothe handling necessary in the conventional process, and consistentquality control is difficult.

SUMMARY

What is needed is a microcoil that can be manufactured more easily andwhich results in a more uniform microcoil with more consistent quality.What is also needed is a microcoil made by attaching a conductor onto aninsulating film and configuring the film to form a winding or multiplewindings. The manufacturing process of the microcoil requires minimalprocessing steps and minimal exposure to handling damage duringprocessing. The process of manufacturing the microcoil is also conduciveto tight quality control standards yet it is easily adapted toaccommodate product design changes. The novel manufacturing process iscapable of producing a novel microcoil that is extremely small andinexpensive, with a high manufacturing yield.

Microcoils produced by this process could be round or have other shapesdepending on the mandrel or form that the film wraps around. A microcoilcan be formed by soldering an end of the film to the mandrel and turningit to wrap the film into a winding. Multiple windings could also beincluded in one microcoil to make a series of connected windings.

In a further embodiment of the invention, the conductor is deposited asa trace onto the film using lithography and sputtering depositiontechniques. The shape of the resulting microcoils is easily controlledby changing the mask pattern for the conducting trace deposited on thefilm. The electrical properties of the trace of conducting material areeasily controlled by varying the trace material, and the width/thicknessof the trace.

The microcoil might be applied with a medical device such as a catheterwhere the catheter is guided by magnetic resonance imaging using themicrocoil. The microcoil might be further combined with other electricaldevices nested at least partially inside the coil.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a top view of a trace unit in a flat condition.

FIG. 2 is a sectional view along line 2-2 of the trace unit in a flatcondition in FIG. 1.

FIG. 3 a is a perspective view of a trace unit and a mandrel.

FIG. 3 b is a perspective view of a trace unit being rolled onto amandrel.

FIG. 4 a is a side view of a microcoil.

FIG. 4 b is a front view of a single winding of a microcoil.

FIG. 4 c is a sectional view along line 4 c-4 c of a single winding inFIG. 4 b.

FIG. 5 is a perspective view of a microcoil.

FIG. 6 is a perspective view of a catheter device.

FIG. 7 is a close up view of an end of a catheter device.

DESCRIPTION OF THE INVENTION

A catheter 100 is shown in FIG. 6, is used to probe areas of interestinside a patient. The distal end 101 of the catheter 100 can be insertedby controls at its proximal end 102. In order to image the area ofinterest, and potentially steer the distal end 101 of the catheter tothe desired location, it is helpful to include an MR microcoil 60 at thedistal end 101 of the catheter 100. The microcoil 60 uses magneticresonance imaging techniques to characterize the tissue in its immediatevicinity. Signals from the microcoil 60 are sent along a length 104 ofthe catheter 101 through an electrical channel 103 to the proximal end102 of the catheter where they can be used by the surgeon to indicatewhere the distal end 101 of the catheter is, and what types of tissueare near the distal end 101.

A microcoil 60 as shown in FIG. 5 is manufactured by rolling a traceunit 10 as shown in FIG. 1 in such a way as to form at least one winding70. A preferred embodiment of the microcoil 60 contains both a firstwinding 70, and a second winding 75 electrically connected and spacedapart by a joining portion 39. The microcoil 60 and method for formingthe microcoil 60 are described in detail below.

FIG. 1 shows a trace unit 10 that is comprised of a flexible film 20, aconducting trace 30, and an attaching trace 45. As shown in FIG. 2, theflexible film 20 has a thickness 21 and the conducting trace 30 has athickness 46. In a preferred embodiment, the thickness 21 and thethickness 46 are constant across the trace unit 10, however, thethickness 21 and the thickness 46 may vary in alternate embodiments. Theflexible film 20 may have several shapes. It may be continuous, or itmay contain openings in the film in areas other than where it supportsthe conducting trace 30.

Looking again at FIG. 1, the conducting trace 30 can be further brokendown into a first leg 31 having a first leg length 32 and a second leg33 having a second leg length 34. The first leg 31 has a lead end 41 anda joining end 42, and the second leg 32 also has a lead end 43 and ajoining end 44. The first leg 31 and the second leg 33 have a tracewidth 49, which is uniform throughout the legs in a preferredembodiment.

The first leg 31 and the second leg 33 are substantially parallel to atrace unit axis 11 of the trace unit 10. However, as shown in FIG. 1,they are not exactly parallel to the trace unit axis 11. The legs 31 and33 are shown in a preferred embodiment in FIG. 1 as having a slightcurve, with the curve being more pronounced near a joining portion 39.The orientation of the legs 31 and 33 as shown in FIG. 1 is only onepreferred embodiment. One skilled in the art would recognize thatseveral configurations of legs would be possible to form other preferredembodiments without departing from the scope of the invention.

The conducting trace 30 also includes a first lead 35 and a second lead37, having a first lead length 36 and a second lead length 38, and afirst lead width 47, and a second lead width 48. The width of traceelements such as the legs and leads can be varied between elements, andwithin elements to alter the electrical characteristics of the trace.For example, a lead 35 could be wider than a leg 31, or a leg 31 couldhave a varying width along its length 32.

The first and second leads 35, 37 are attached to the first and secondlegs 31 and 33 at the first and second leg lead ends 41 and 43respectively. The leads 35 and 37 may alternatively be attachedelsewhere along the conducting trace 30 without departing from the scopeof the invention. Supplemental leads (not shown) may also beelectrically connected to the conducting trace to give device feedbackor insert device instructions. The two legs 31 and 33 are joined attheir respective joining ends 42 and 44 by a joining portion 39 of theconducting trace 30. The joining portion 39 has a length 40.

The trace unit 10 also includes an attaching trace 45 located adjacentto the joining portion 39. The attaching trace 45 is electricallyisolated from the conducting trace 30. In a preferred embodiment, theattaching trace 45 is parallel with the joining portion 39 of the traceunit 10. In a preferred embodiment, the attaching portion is alsosubstantially perpendicular to the legs 31 and 33.

The conducting trace 30 is comprised of copper because of its highconductivity and ductility. The ductility allows the copper to be rolledwithout cracking or breaking or otherwise causing an electrical failure.Any other conducting material that satisfies these conditions would beacceptable. The flexible film is comprised of polyimide because itexhibits good insulating properties and is readily available. It is alsoflexible, and withstands the deposition process used to attach theconducting trace. Any other flexible insulating material would beacceptable.

The conducting trace is attached to the flexible film by using a sheetof conductor, adhesive, and a basic lithography or photolithographytechnique commonly known in the industry. First a sheet of copper isadhered to the flexible film using a suitable adhesive. A mask layer isthen deposited onto the sheet of copper with a positive image of theconducting trace 30 and the attaching trace 45. The flexible film 20 andthe mask layer are then exposed to an etching chemical capable ofremoving copper, which removes the copper in the unmasked regions of thesheet. Once the excess copper is removed from the flexible film 20, themask layer is removed to leave behind only the flexible film 20, theconducting trace 30, and the attaching trace 45. While this method ofattaching the conducting trace 20 and the attaching trace 45 ispreferred, it should be noted that any of several methods for attaching,including sputtering, physical vapor deposition, chemical vapordeposition, or mechanical attachment could be used to produce theinvention.

In alternative embodiments, additional layers of flexible insulator andareas of conducting material may be attached and deposited onto theflexible film 20. Additional layers of flexible insulator may be used toprotect the conducting trace 30, or they may be used to isolateadditional areas of conducting material from the conducting trace 30.Additional areas of conducting material may be used to form electricaldevices such as capacitors, integral with the trace unit 10.

The trace unit 10 is next prepared for rolling by attaching the traceunit 10 to a mandrel 50 as shown in FIG. 3 a. The mandrel 50 may beround or square or any of several variations in cross section. Themandrel 50 may also be solid or hollow. The mandrel 50 may be made fromany of a number of materials such as plastic or glass or non-magneticmetal. The mandrel 50 may not include magnetic materials due tointerference with the magnetic resonance imaging that the coils aredesigned for in end use. The mandrel 50 may also be made up of more thanone material. In this embodiment, the mandrel 50 is a semi-rigid coaxialline that is comprised of silver-plated copper on its outside diameter.The semi-rigid coaxial line is electrically conductive which allowsinformation from the coil to be transmitted back to the user through thecoaxial line.

A preferred manufacturing process of the microcoil 60 begins when thetrace unit 10 is attached to the mandrel 50 by soldering the attachingtrace 45 to the outside diameter of the mandrel 50. The attaching trace45 is soldered such that it is parallel with a longitudinal axis 51 ofthe mandrel 50. More importantly, the attaching trace 45 and mandrel 50are oriented such that when rolled, the legs 31 and 33 of the conductingtrace 30 form windings 70 and 75 as shown in FIG. 5. Although a mandrel50 is used to roll the trace unit 10 in a preferred embodiment, thetrace unit 10 may be rolled without using a mandrel 50 without departingfrom the scope of the invention.

In a preferred manufacturing process, once the trace unit 10 is attachedto the mandrel 50, the mandrel is rolled about the longitudinal axis 51in direction 52 as shown in FIG. 3 b. In a preferred embodiment, therolling of the trace unit 10 about the mandrel 50 forms a microcoil 60comprised of a first winding 70 and a second winding 75 as shown in FIG.5, one winding formed from each leg 31 and 33. The joining portion 39electrically connects the pair of windings 70 and 75. Alternativeembodiments could form only one winding, which would not require ajoining portion, or several windings could be formed, which wouldrequire multiple joining portions.

Design variations of the resulting microcoil 60 are easily accommodatedwith a preferred manufacturing process. The number of turns in thewindings 70 and 75 may be controlled by varying the lengths 32 and 33 ofthe legs 31 and 33 respectively when forming the conducting trace 30 onthe trace unit 10. Alternatively, the diameter 53 of the mandrel 50 thatis chosen can be varied to change the resulting number of turns. Nineturns are used for a preferred embodiment.

As shown in FIG. 5, a longitudinal winding spacing 61 between windings70 and 75 in the microcoil 60 is controlled by varying the length 40 ofthe joining portion or portions 39 when forming the conducting trace 30on the trace unit 10.

FIG. 4 a shows a side view of the microcoil 60. In this side view onlythe first winding 70 of the microcoil 60 is visible. The first winding70 is further shown in FIG. 4 b and sectional view 4 c of FIG. 4 b. Asshown in FIG. 4 c, within a given winding, a radial trace spacing 71 iscontrolled by selecting or varying the thickness 21 of the flexibleinsulating film 20. Also, a longitudinal axis trace spacing 72 iscontrolled by varying the shape and orientation of the legs 31 and 33 onthe trace unit 10.

As shown in FIG. 3 a, the legs 31 and 33 are substantially perpendicularto the longitudinal axis of rolling 51. However, the degree ofperpendicularity varies along the legs 31 and 33. In a preferredembodiment, a given portion of a leg near the attaching trace 45 is lessperpendicular to the longitudinal axis of rolling 51 than a portion of aleg proximal from the attaching trace 45. For example, the orientationof a generally linear leg could be varied such that the angle thegenerally linear leg makes with the longitudinal axis of rolling is moreor less than 90 degrees. The shape of a leg could also be varied suchthat a leg is more linear or more arc shaped. These shape andorientation variations translate into variations of the longitudinalaxis trace spacing 72.

Once the rolling of the trace unit 10 is complete, a microcoil 60 hasbeen formed. A temporary retaining band 80 may then be placed around themicrocoil 60 to hold its shape during the final placement of themicrocoil 60 into its associated medical device. After the leads 35, 37and possibly supplemental leads have been electrically connected to themedical device, the temporary band 80 may be removed. A more permanentprotective oversleeve 90 as shown in FIG. 7 is then used to protect themicrocoil and to hold its shape. If needed, other electrical componentsuch as capacitors (not shown) may be embedded or partially embeddedinside the structure of the microcoil 60.

As shown in FIGS. 6 and 7, a catheter device 100 is used in a preferredembodiment. The catheter device 100 has a distal end 101 and a proximalend 102. The microcoil 60 is located at the distal end 101 of thecatheter. In operation, data from the microcoil travels along the length104 of the catheter 100 through an electrical channel 103. A continuingelectrical channel such as a coaxial line (not shown) transmits the datafrom the electrical channel 103 to another device such as a monitordevice. This device receives information from the microcoil 60concerning location of the distal end 101, or concerning the nature andcondition of the tissue near the distal end 101.

Although specific embodiments have been illustrated and describedherein, it will be appreciated by those skilled in the art that anyarrangement which is calculated to achieve the same purpose may besubstituted for the specific embodiment shown. This application isintended to cover any adaptations of variations of the presentinvention. It is to be understood that the above description is intendedto be illustrative, and not restrictive. The scope of the inventionincludes any other applications in which the above structures andfabrication methods are used. The scope of the invention should bedetermined with reference to the appended claims, along with the fullscope of equivalents to which such claims are entitled.

The foregoing description of the embodiments has been provided forpurposes of illustration and description. It is not intended to beexhaustive or to limit the disclosure. Individual elements or featuresof a particular embodiment are generally not limited to that particularembodiment, but, where applicable, are interchangeable and can be usedin a selected embodiment, even if not specifically shown or described.The same may also be varied in many ways. Such variations are not to beregarded as a departure from the disclosure, and all such modificationsare intended to be included within the scope of the disclosure.

1. A method for forming a microcoil comprising: attaching a trace ofconductive material to a film of insulating material; affixing anattaching trace to the film, wherein the attaching trace is electricallyisolated from the trace of conductive material; operably coupling theattaching trace to a mandrel prior to rolling of the mandrel; androlling the mandrel with the film attached to circumferentially wrap thetrace of conductive material more than one revolution around alongitudinal axis of rolling.
 2. The method for forming a micro coil ofclaim 1 wherein said attaching the trace of conductive materialcomprises adhering a sheet of conductive material to the film ofinsulating material, masking the sheet of conductive material with amasking material, etching the sheet of conductive material, and removingthe masking material.
 3. The method for forming a microcoil of claim 1wherein the trace of conductive material includes copper.
 4. The methodfor forming a microcoil of claim 1 wherein the film of insulatingmaterial includes polyimide.
 5. The method for forming a microcoil ofclaim 1 wherein the mandrel comprises a round cross section.
 6. Themethod for forming a microcoil of claim 1 wherein the mandrel is hollow.7. The method for forming a microcoil of claim 1 wherein the mandrelcomprises a semi-rigid coaxial conductor.
 8. A method for forming amicrocoil comprising: attaching a trace of conductive material to asubstantially planar film of flexible insulating material; affixing anattaching trace to the film, wherein the attaching trace is electricallyisolated from the trace of conductive material; operably coupling theattaching trace to a mandrel prior to rolling of the mandrel; androlling the mandrel with the film attached such that, when rolled, theend of the film is pulled, and the trace of conductive materialcircumferentially wraps around a longitudinal axis of rolling.
 9. Themethod for forming a microcoil of claim 8, wherein said attaching thetrace of conductive material further comprises adhering a sheet ofconductive material to the substantially planar film of flexibleinsulating material, masking the sheet of conductive material with amasking material, etching the sheet of conductive material, and removingthe masking material.
 10. The method for forming a microcoil of claim 8wherein the trace of conductive material includes copper.
 11. The methodfor forming a microcoil of claim 8 wherein the substantially planar filmof flexible insulating material includes polyimide.
 12. The method forforming a microcoil of claim 8 wherein the mandrel comprises a roundcross section.
 13. The method for forming a microcoil of claim 8 whereinthe mandrel is hollow.
 14. The method for forming a microcoil of claim 8wherein the mandrel comprises a semi-rigid coaxial conductor.
 15. Amethod for forming a microcoil comprising: attaching a trace ofconductive material to a film of insulating material, the trace ofconductive material including a leg; operably coupling the film to amandrel; and rolling the mandrel with the film attached about alongitudinal axis to thereby circumferentially wrap the trace ofconductive material more than one revolution around the longitudinalaxis and to thereby extend the leg progressively radially outward fromthe longitudinal axis.
 16. The method of claim 15, further comprisingcoupling an attaching trace to the film, wherein the attaching trace iselectrically isolated from the trace of conductive material, and whereinoperably coupling the film to the mandrel includes operably coupling theattaching trace to the mandrel prior to the rolling of the mandrel. 17.The method of claim 16, wherein operably coupling the attaching trace tothe mandrel includes soldering the attaching trace to the mandrel. 18.The method of claim 15, wherein the trace of conductive material furtherincludes a lead electrically coupled to the leg, and wherein rolling themandrel includes extending the lead substantially parallel to thelongitudinal axis.
 19. The method of claim 15, wherein the trace ofconductive material includes a first leg and a second leg that areelectrically coupled together via a joining portion, and wherein rollingthe mandrel includes extending each of the first and second legsprogressively radially outward from the longitudinal axis and extendingthe joining portion substantially parallel to the longitudinal axis. 20.The method of claim 15, further comprising operably coupling themicrocoil to a distal end of a catheter.